A significant bottleneck in the loud speaker arts is the provision of good audio response to the lower audio frequencies. It is a challenge to produce good low frequency response in general, and this challenge is much greater when any attempt is made to miniaturize a speaker system. Thus, one answer to low frequency response from a speaker system is to provide larger speaker diaphragms with longer pumping strokes. However such speakers occupy a large area, and provide other problems including the ability of the speaker transducer driving coils to withstand the large currents necessary for producing the necessary high amplitude power for lower audio frequency range sound reproduction.
Furthermore fidelity of audio signal reproduction is always a problem, and especially with the lower audio frequencies. Even the provision of larger speaker diaphragm diameters does not assure good reproduction because cabinet mounts are critical to the faithful reproduction of audio from the electric current signals used to driver speaker transducers. Similarly, the ability of the speakers to project the sound outwardly over reasonable distances is a problem. The mount of a speaker at an opening in a speaker cabinet especially causes problems of faithful reproduction and reasonable projection out into a room of any significant size.
Recent trends into compact sized systems has caused even greater problem with reproduction in the low frequency audio signal range. Everything natural and normal about cabinetry leads to larger dimensions for lower range audio signal reproduction. There has been no acceptable performance compact cabinet systems available for acceptable reproduction fidelity of the lower audio frequencies.
Typical speaker systems of the prior art are exemplified by the following prior art U.S. patents, now briefly discussed.
In an attempt to improve bass reproduction quality, H. Deutsch, U.S. Pat. No. 4,251,687, Feb. 17, 1981 provides a cabinet resonant at selected frequencies to communicate with a simulated exponential horn passageway for the audio wavefront. For very low audio frequency response these cabinets would be very large and thus the low frequency bass speaker is not resonated but directly faces a housing opening.
H. S. Knowles, U.S. Pat. No. 2,295,483, Sept. 8, 1942 has provided a speaker system for lower audio frequency reproduction having a closed non-resonant compartment enclosing the speaker diaphragm back surface and isolating it from the projected sound out of a horn coupled to the speaker front surface. The dimensions of such a horn for a large diameter woofer speaker would be prohibitive in size.
J. Weckler, U.S. Pat. No. 4,807,293, Feb. 21, 1989 provides a cabinet with a built in horn type construction for low frequencies derived from a partially damped speaker diaphragm back side while the higher frequencies are directly projected from the front side. Objectives were to reduce the amplitude of the speaker membrane movement and to produce low frequency response in the order of 40 Hz in a small loudspeaker housing. These are substantially the same objectives as the present invention. However, the front diaphragm side of the speaker is the one designed to reproduce and project the lower frequency audio waves using the pumping action of the diaphragm, and thus, particularly when the back side is also necessarily damped, there can be no significant amplitude of low frequency volume reproduced in such a system in response to a reasonable amount of electric driving current.
A housing with a multiplicity of speakers positioned with front diaphragm surfaces facing outwardly in one wall is disclosed by T. R. Karson, U.S. Pat. No. 4,224,469, Sept. 23, 1980 wherein the front is isolated from that of the tweeter and midrange speakers to avoid interaction by a reflecting loading chamber for the backside diaphragm sound forming a folded transmission line non-resonating cavity of sufficient size. This speaker cabinet system requires a very complex and critical arrangement and distribution of different audio frequency ranges amongst the various speakers and cabinet sub-compartments.
It is therefore an object of this invention to overcome these prior art deficiencies and to provide an improved compact woofer speaker cabinet system which faithfully reproduces low frequency audio signals, typically 35 Hz, and projects them with high amplitude over significant distances. Other objects, features and advantages of the invention will be found throughout the following description, drawings and claims.